Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Housed microphone
Reexamination Certificate
2002-03-29
2004-04-13
Kuntz, Curtis (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Housed microphone
C381S356000, C381S361000, C381S368000, C381S360000
Reexamination Certificate
active
06721432
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a microphone used in a video camera etc.
BACKGROUND ART
There has conventionally been available such a directional microphone used in a video camera etc. as follows. That is, this microphone includes a capacitor microphone unit and an amplification circuit board housed and disposed in a cylindrical housing having a structure enhancing directivity and also houses and disposes this cylindrical housing in an outer cylinder. Between the cylindrical housing and the capacitor microphone unit is sandwiched vibration preventing rubber. Likewise, between the cylindrical housing and the outer cylinder is also disposed vibration preventing rubber. In such a configuration, an audio signal converted into an electric signal by the capacitor microphone unit is amplified by the amplification circuit board and then issued to the outside. It should be noted that the cylindrical housing houses a battery therein in some cases.
This prior art microphone, however, suffers from a problem of occurrence of an interference sound caused by an electromagnetic wave. The interference sound here refers to the following. That is, it refers to a noise sound superimposed on a recorded speech sound which occurs due to a high-frequency component contained in an external electromagnetic wave when the speech sound is recorded by a microphone.
With recent prevalence of portable telephones, there have been increasing such cases that many unspecified persons including reporters using a microphone use those portable telephones in communication at a recording site requiring a microphone. In particular, if a reporter uses his portable telephone while recording a variety of speech sounds, he would use his microphone and portable telephone in such a state where they are very close to each other. Such a use situation of a microphone may occur on an every-day basis in the future too when a news site is reported using a video camera etc. having a built-in microphone.
Although an influence of an electric field generated by a portable telephone reaches relatively short, it is known that in its vicinity (within a few to few tens of centimeters therefrom), that field has a very high strength of a few tens of volts/meter, which is a few tens of thousands of times as much as that generated over the cities by a commercial radio wave.
If a microphone and a portable telephone are used as being very close to each other, an electromagnetic wave generated by the portable telephone has a remarkable influence on the microphone, so that an interference sound is mixed into an audio signal. This is described specifically as follows.
A microphone can be considered to be an operation circuit of an FET transistor the gate of which serves as a diaphragm of a capacitor microphone unit. In the operation circuit of such an FET transistor, a vibration generated by a sound pressure of speech sound is captured as a potential induced across an electret film which constitutes the diaphragm. Accordingly, in the microphone, a sound-pressure deviation is captured as a voltage deviation, which is in turn taken in as a change in voltage input to the gate of the FET transistor. The change in voltage input thus taken in is used as an audio signal input to thereby operate the microphone.
If a high-frequency strong electric field occurs near a microphone unit having such characteristics, a nonlinear distortion occurs in an input/output circuit or other electric circuits of the electret film or FET transistors, so that an envelope detected-wave output of a frequency-modulated, amplitude-modulated, and digital-modulated high-frequency signals appears in an audio band. Further, a similar detected-wave output appears also at a subsequent-stage amplification circuit board. Such a detected-wave output gives rise to various high-frequency interference sounds in the audio signal.
The recent prevalence of portable telephones has been shifting a service frequency band toward a higher frequency side (e.g., 1.5 GHz), so that presently an influence of electromagnetic waves on such a microphone is becoming more and more remarkable. Accordingly, there is desired such a microphone that is not easily influenced by electromagnetic waves.
Also, to prevent beforehand any disturbance due to malfunction etc. of a variety of electronic apparatuses caused by an electromagnetic wave, many counties have laws ahd regulations of the electrbmagnetic-wave resistance of such electronic equipment. One example is CE (Conformite Eoropeenne) in Europe. Further, with prevalence of high-electromagnetic-wave generators used by individuals represented by a portable telephone, many countries are trying to prevent beforehand the future-expected disturbance caused by an electromagnetic wave by further tightening those laws and regulations so that only such products that have a higher electromagnetic-wave resistance may be allowed to circulate in the world markets. In view of such a status quo, the microphone is also desired to have an even higher electromagnetic-wave resistance.
To solve the above-mentioned problems, the prior-art microphone is also provided with a grounding path for connecting a grounding part thereof to the ground. This grounding path, however, is comprised of a lead wire for interconnecting the microphone unit and the amplification circuit board, a grounding wiring line in the amplification circuit board, and a lead wire for interconnecting the amplification circuit board and a microphone cable, so that it cannot be the shortest path effective enough to remove an interference sound caused by a high-frequency electric field.
A In view of the above, it is an object of the invention to provide a microphone unit which can effectively remove an interference sound caused by a high-frequency electric field.
SUMMARY OF THE INVENTION
A microphone or a video camera according to the invention includes a microphone unit, a cylindrical housing made of a conductor for housing the microphone unit, and an intermediate connector which electrically connects a grounding part of the microphone unit to the cylindrical housing along essentially the shortest path while blocking mechanical vibrations. In this configuration, it operates as follows.
Even if an electric field induced by an electromagnetic wave present around the microphone is formed in the cylindrical housing to correspondingly cause such a high-frequency signal to occur in the microphone unit that contains a modified signal which gives an interference sound to the microphone, the high-frequency signal is led through the intermediate connector to the cylindrical housing along essentially the shortest distance. By grounding the cylindrical housing beforehand, therefore, such a high-frequency signal occurring at the microphone unit can be securely discharged to the ground through the cylindrical housing. Moreover, the cylindrical housing, which is a conductor having a simple construction and also which has a vibration preventing mechanism between itself and an outer cylinder, serves to connect the microphone unit to the ground potential therethrough along essentially the shortest path not longer than necessary. This configuration enables to securely decrease the interference sound caused by such a high-frequency signal as mentioned above.
It should be noted that the cylindrical housing has a simple construction and so is liable to be exposed to the outside at part of a peripheral surface or end thereof, so that it can be grounded relatively easily.
Also, in the improved microphone of the invention, the intermediate connector is made of an elastic short-hair-shaped conducting member, which itself is protruded from either one of the microphone unit and the cylindrical housing as having its tip abutted against the other. In this configuration, the following is possible.
The short-hair-shaped conducting member can give a sufficient function required on the intermediate connector of electrically interconnecting the two while blocking the mechanical vibrations and also can be mounted relatively simply.
Kuntz Curtis
Matsushita Electric - Industrial Co., Ltd.
McDermott & Will & Emery
Nguyêñ Tuân D
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